Telecommunications employs the transmittal of data over a distance. A given transmission may travel over a common electrical wire, a fiber optic cable, a terrestrial microwave link, or even a satellite link; indeed, most distant transmissions use more than one of these media as they travel from sender to receiver. However, most equipment at the receiving or transmitting end of a signal connects to an electrical wire, usually because of simplicity, cost, and the lower bandwidth requirements of end equipment.
Two types of wires are most commonly used for connecting data lines to end equipment. The first is the twisted-pair conductor (see FIG. 1), which consists of two thin, insulated electrical conductors 20, 22 twisted together in a helical fashion. The second is the coaxial conductor (see FIG. 2), which consists of a single insulated center conductor 24 surrounded by a braided conducting sheath 26 and an outer, insulating protective covering 28. The twisted-pair conductor enjoys a price advantage over the coaxial conductor. The twisted-pair conductor also occupies less space, such that several twisted pairs can be bundled in a cable roughly the size of one coaxial conductor. The coaxial conductor also has advantages; for example, it is less fragile and better suited for high-bandwidth communications.
Twisted pairs generally operate in a differential mode, while coaxial conductors operate in a single-ended mode. In differential mode, a positive signal change on one wire is coupled with an equally negative signal change on its pair. This differential signal reduces radiated noise from the twisted pair. In contrast, single-ended transmission occurs over a single wire between two devices sharing a common ground connection. With a coaxial cable, the center conductor provides a signal path and the braided sheath is generally tied to the equipment chassis ground. The differential mode of transmission is commonly termed "balanced" because both wires act equally in sending a signal, while the single-ended mode is known as "unbalanced" because a single wire carries the signal.
Equipment suppliers have historically offered either a balanced or an unbalanced connection on a single system. Some suppliers have also offered systems that have dual connection ports, with the customer being responsible for removing a cover from a unit and installing one or more internal jumpers to complete the system configuration.